The present invention relates generally to instruments for use in electrosurgical techniques. More specifically, the invention relates to electrosurgical instruments made of conducting ceramics or cermets and the use and manufacture of these instruments.
Electrosurgery has become an important alternative to conventional surgical techniques and offers many unique advantages over the traditional procedures. In electrosurgery, an electric current is used to cut or cauterize human or animal tissue. Presently, there are two main types of electrosurgical apparatus in use. Depending on the number of electrodes used in the cutting and cauterization these instruments are called unipolar or bipolar.
In a unipolar electrosurgical apparatus, current (usually "RF" current) is supplied to an electrode which is used to cut or cauterize the tissue. When in use, current flows through the electrode to the patient and the circuit is completed using a "patient plate" on which the patient lies. The surface area of the electrode through which current flows (the "active electrode surface") is small relative to the area of the patient plate and therefore an intense local current density is generated at the electrode. This results in cutting or cauterization of the tissue in the immediate proximity of the electrode. An example of a unipolar electrosurgical instrument is described in U.S. Pat. No. 4,927,420, which is incorporated herein by reference.
In a bipolar electrosurgical apparatus, the "patient plate" of the unipolar apparatus is replaced by a second electrode separated from the first electrode by a small gap. In operation, an intense local current density is generated between the electrodes and this results in cutting or cauterization of the tissue between the electrodes. Examples of bipolar electrosurgical instruments are described in U.S. Pat. Nos. 5,396,900, 5,217,458, 5,342,381, and 5,395,369, all of which are incorporated herein by reference.
The electrodes used in both unipolar and bipolar apparatus come in a wide variety of shapes, sizes, and configurations. Depending on the surgical requirements, the electrodes can be in any of a variety of shapes such as needles, loops, spatulas, scalpel blades, scissors, forceps, and balls. Electrosurgical techniques have also been extensively used for endoscopic surgery. Since electrosurgical tools can be made much smaller than their conventional counterparts, electrosurgery is especially suited to this type of surgery. A wide variety of shapes and configurations of endoscopic electrodes have been described. See for example U.S. Pat. Nos. 5,396,900, 5,217,458, and 5,395,369.
In conventional electrosurgical instruments the active electrode surfaces are usually made of stainless steel ("SS"). However, there is a well known drawback to using such SS electrodes; namely, that burnt tissue layers adhere to the electrode surface during the electrosurgical procedure. It is thought that the mechanism that causes tissue to stick to the instruments is as follows.
During electrosurgical procedures, an intense electric current density is generated between the electrodes and the tissue. In fact, the electrosurgical procedure often causes arcing between the electrode and the tissue. The high current density causes intense heating which carburizes the tissue and results in the required cutting or cauterization. The electrodes of the conventional instruments react with this carburizing atmosphere and this forms adherent burnt tissue layers on the surface of the electrodes. During the electrosurgical procedure, burnt tissue begins to build up on the instrument surfaces in the form of a black film. When this buildup is thick enough to sufficiently reduce the current density between the electrode and the tissue, the tissue coming into direct contact with the hot black film will stick. The surgeon is then forced to stop the operation and clean the electrosurgical instrument. This cleaning can require enough force to scratch the surface of the SS. Such scratches roughen the surfaces of the instrument and this in turn causes tissue residue to build up faster and results in more sticking.
An additional drawback of the conventional instruments is that the electrosurgical procedure heats the electrodes and since SS is a relatively poor thermal conductor the instrument rapidly heats up to very high temperatures (&gt;500.degree. F.). Furthermore, the electrosurgical procedure also transfers some of the metal to the tissue which pits the surface of the metal electrode and contaminates the wound. The composition of the stainless steel electrodes includes iron, nickel, and chromium which may be deposited into the wound with harmful consequences. The pitting of the electrode surface also further roughens the surface and therefore exacerbates the problem of tissue buildup.
Many electrosurgical instruments also include non-conducting ceramics (used as insulating elements) in addition to metal electrodes. These ceramics are typically oxide ceramics which, in the carburizing environment present during the electrosurgical procedure, also react and form adherent tissue layers. There have been many attempts made to overcome the problem of tissue buildup in the conventional apparatus. For example, the metal electrodes have been coated with an organic material, usually a Teflon material or another polymer. Unfortunately, these low melting, volatile materials cannot withstand the high localized temperatures of the electric discharge between the electrode surface and the tissue. The resulting products of these melted/vaporized coatings are known to form harmful chemicals and undesirable products are deposited into the cut/cauterized wounds. Surgical staff have reported that after exposure to these vaporized organic coatings, flu-like symptoms result (this problem has been termed "polymer fume fever" or "teflon flu"). A further disadvantage is that a coating of organic material is melted in the very early stages of the electric discharge and therefore provides little or no improvement in the reduction of tissue adhesion. It is typical for the surface of a conventional SS electrode to be roughened (prior to conventional coating with Teflon material) to improve the mechanical bond between the SS and the coating, and in this case only a roughened metal surface remains following the initial discharge, thereby promoting increased pitting of the metal surface. This pitting also results in transfer of the metal from the electrode to the tissue.
Another proposed solution to the problem of tissue adhesion is the use of a vibrating blade. Such a solution is disclosed in U.S. Pat. Nos. 4,674,498, 4,802,476, and 4,922,903. These references describe electrosurgical apparatus including means for vibrating an electrosurgical blade during use to prevent buildup of tissue and debris on the blade. This technique requires the apparatus to include a means for vibrating and a means for coupling the vibrations to the electrosurgical instrument. This increases the cost and complexity of the apparatus and in some cases, for instance endoscopic surgery, may present great technological problems.
In U.S. Pat. No. 4,927,420 Newkirk et al. describe the use of an ultrasharp metal needle (composed of any of a variety of refractory alloys) in electrosurgery. The use of an ultrasharp needle is said to allow use of lower RF power which reduces scarring and helps eliminate drag (tissue buildup) when cutting tissue. However, the elimination of drag in using such a needle relies on being able to use reduced RF power which in turn relies on the use of an ultrasharp needle. Thus the teaching of U.S. Pat. No. 4,927,420 is severely limited in the range of shapes of electrosurgical instruments to which it may be applied.
The use of refractory metal electrodes is also disclosed by Grabinger et al. in U.S. Pat. No. 4,850,353 which describes the use of refractory metal conductive strips attached to an insulating ceramic substrate.
Ceramics have been used extensively in electrosurgical instruments, however, these materials have always been nonconducting ceramics that have specifically been used for insulating the metal electrodes. Such arrangements have been described, for example, in U.S. Pat. Nos. 4,862,890, 4,958,539, 5,071,419, 4,850,353, 5,192,280, 5,396,900 and 5,007,908. In all previous electrosurgical instruments of which the inventor is aware, the active electrode surface through which the current flows is made of metal or polymer coated metal and not ceramic.
From the foregoing discussion it is obvious that there exists a basic problem in electrosurgery; namely, the buildup of tissue on electrosurgical instruments during the electrosurgical procedure. Although some solutions to this problem have been proposed, these all have their own drawbacks. There is therefore a need for electrosurgical instruments to which tissue does not adhere, and which can be formed in a wide variety of shapes. Furthermore, there is a need for electrosurgical instruments to which tissue does not adhere and which function without the instrument being coupled to any external mechanical vibrating means.